The invention relates to a cartridge for recoilless training weapons, more particularly to a training bullet contained in a cartridge case and having a closed charge case connected to the cartridge case and fitted with an end cup at the back to enclose a spotting charge and a counter-mass to be expelled from the charge case.
Such a training cartridge is known from the German patent publication No. DE-OS 34 21 841. The training cartridge is fired from a modified training weapon otherwise used for anti-tank defense and consists of a subcalibre practice round contained in a cartridge case and, in diameter, a larger charge case linked to it, in which a charge, the so-called spotting charge, is stored to expel a counter-mass, whereby the spotting charge is ignited when firing the practice round. Glass sand is used as the counter-mass, where necessary with a low proportion of a lubricant such as zinc stearate.
The charge case is closed off at the back end by a cover, the so-called end cup. This cup is, for example, formed from thin aluminium sheet and has a running edge which borders with the back end of the charge case
One problem when firing such practice rounds is that the end cup is deformed by the shock wave of the spotting charge before the dish and counter-mass are blasted backwards out of the charge case. What can happen is that at least one part of the counter-mass clots in the deformed case, quasi forming a cup, and together they are almost fired like a bullet out of the training weapon into the open. This clotting of the counter-mass occurs on the one hand in a relatively wide dispersing angle area up to 120.degree. and moreover with such force that a 1 mm thick grey board is penetrated at a distance of 20 m. This is unacceptable for safety reasons, due to the increased risk of injury to persons standing behind the training weapon.
To find a solution, it was proposed to provide the end cup with predetermined breaking points, e.g. in the form of material dilution starting from the centre either radially or star-shaped. It is, however, difficult in manufacturing terms to guarantee a tearing of the predetermined breaking point with a defined force. Moreover, the tearing force of the predetermined breaking point is temperature-dependent, the slighter the higher the temperature. This has several consequences:
If the predetermined breaking point tears unevenly on firing, for instance, due to existing production inaccuracies, this can have repercussions on the shock wave of the spotting charge within the charge case and a certain proportion of the pressure forces is directed at the wall of the charge case so that parts of the counter-mass are pressed more forcibly against the wall. As a result of the increased friction between the wall and the counter-mass, there is increased side abrasion and, consequently, undesired different recoil forces.
If the predetermined breaking point is so designed that the practice round passes a drop test, in which the practice round is dropped onto a hard surface from a height of 2 m and is not damaged at temperatures up to +60.degree. C.--in particular the predetermined breaking point of the end cup must not tear--then the danger is that the predetermined breaking point does not tear or does not do so at the correct moment during firing at -40.degree. C., so that undesired high recoils occur. If the predetermined breaking point, on the other hand, is so designed that it will definitely tear at low temperatures, then the danger exists that it will not pass the drop test when warm.
Apart from that, a certain cup shaping of the dish or parts of it can occur in this formation of the end cup with predetermined breaking points, and thus clot formation of the counter-mass cannot be completely prevented.